When an Oregon contracting company won a bid to install 4,100 feet of pipeline at depths of 16 to 20 feet below a rocky riverbed, the firm turned to a slide rail system to overcome many of the project’s trench shoring obstacles.
The James W. Fowler Company of Dallas, Oregon, has been working trenching across two sections of the North Santiam River since June 1. The project is part of the City of Salem’s $6 million effort to increase the quantity of potable water that is sent to the city’s water distribution system.
JWF was awarded the job of installing 4,100 linear feet of parallel 69-inch welded steel pipe in 40-foot joints, concrete flowmeters, chemical feed vaults, pressure sensors, valves and appurtenances. The project is scheduled for completion by May 31.
Site conditions
Project specs called for the pipeline to run at depths varying from 16 feet to more than 20 feet in sand and cobbles. A free flowing water table at 6 feet below the existing grade required continuous dewatering. Large diameter river rock clogs the North Santiam making sheet piling the river crossing an unacceptable option. The pipeline also runs adjacent to existing fluoridation and disinfection buildings. Vibration during installation posed a risk of structural damage to those buildings.
Selecting a shoring system
JWF employees evaluated the project specs and then researched their trench shoring options. The company decided to rent an Efficiency Production slide rail system from D.P. Nicoli of Tualatin, Oregon.
The slide rail offered the added benefit of simultaneously installing the shoring system while excavating the trench. This would save time and money since the river crossings had to be done at constrained durations. Also due to the precise dimensions and the structural stability of the slide rail, JWF would be able to use the system as a concrete form for pouring the encasement.
“We felt that the river crossings were a good match for an active shoring system,” said JWF project manager Mark Weisensee. “It also eliminated the extra step of sheet piling.”
River crossing
Forty-five days were planned to complete the crossings, so JWF had to use its equipment efficiently and work extended shifts to accommodate the accelerated schedule. JWF is using a Komatsu PC1000, a PC650 and various smaller excavators along with CAT 950 loaders for the excavation and installation of the shoring system and pipeline.
Workers are using the slide rail system in an eight-bay linear configuration. Each bay is 12 feet long and 18 feet wide. All eight bays are installed with sacrificial beams at the bottoms.
Then the parallel 40-foot pipe sections are positioned at depths of 16 to 20 feet. After securing the pipes the spreaders are reinstalled, and the horizontal walers are removed. As the pipeline installation progresses the panels, posts, walers and spreaders that comprise each bay are pulled out concurrently while backfilling the trench.
“The river crossing work was difficult to plan and allocate resources for but through research we learned about the slide rail and we are able to minimize the potential risks,” Weisensee says.
